Hepatobiliary, Pancreas, and Nutrition

Hepatobiliary And Nutrition Reasoning Map

Jaundice questions are best solved by fractionating bilirubin and then placing the block in heme handling. Macrophages degrade heme to unconjugated bilirubin, which travels bound to albumin and is not water soluble. Hepatocytes take it up and conjugate it with glucuronic acid through UDP-glucuronosyltransferase, making it water soluble for biliary excretion. In the intestine, bacteria convert bilirubin to urobilinogen. Some returns to the liver through enterohepatic cycling, some is excreted in urine as urobilin, and most becomes stercobilin in stool.

Unconjugated hyperbilirubinemia results from excess production, impaired uptake, or impaired conjugation. Hemolysis increases unconjugated bilirubin, urine urobilinogen, and stool pigment but does not cause bilirubinuria because unconjugated bilirubin is albumin-bound. Gilbert syndrome is mild reduced conjugation that worsens with fasting, illness, or stress. Crigler-Najjar is severe impaired conjugation. Physiologic neonatal jaundice reflects immature conjugation and increased bilirubin load. Conjugated hyperbilirubinemia is water soluble and can appear in urine.

It results from impaired hepatocellular excretion or cholestasis. Dubin-Johnson syndrome is defective canalicular excretion with a dark liver; Rotor syndrome is similar clinically without dark pigmentation. Extrahepatic obstruction from gallstones, pancreatic cancer, or cholangiocarcinoma causes conjugated bilirubin elevation, pale stools from reduced stercobilin, dark urine, pruritus from retained bile acids, and increased alkaline phosphatase and gamma-glutamyl transferase.

Hepatocellular injury, as in viral hepatitis or toxins, raises AST and ALT more prominently; AST greater than ALT by about 2 to 1 suggests alcohol-associated injury because mitochondrial AST is released and pyridoxal phosphate deficiency lowers ALT activity. Cirrhosis is diffuse bridging fibrosis and regenerative nodules that distort hepatic architecture. Stellate cells in the space of Disse are activated by chronic inflammation, acetaldehyde, oxidative injury, and cytokines, then deposit collagen. Loss of normal sinusoidal flow and increased intrahepatic resistance cause portal hypertension.

Portal hypertension produces portosystemic anastomoses: left gastric to esophageal veins causing esophageal varices, paraumbilical to superficial epigastric veins causing caput medusae, superior rectal to middle and inferior rectal veins contributing to anorectal varices, and retroperitoneal collaterals. Ascites forms from increased hydrostatic pressure, low albumin, splanchnic vasodilation, renal sodium retention, and lymph overflow. Splenomegaly causes thrombocytopenia. Encephalopathy reflects shunting and impaired ammonia detoxification; ammonia is generated by gut bacteria and normally converted to urea.

Lactulose acidifies colonic contents, traps ammonia as ammonium, and increases stooling; poorly absorbed antibiotics reduce ammonia-producing bacteria. Hepatorenal syndrome is functional renal vasoconstriction in advanced liver disease with intense splanchnic vasodilation. Viral hepatitis serology follows viral biology. Hepatitis A is a nonenveloped RNA virus transmitted fecal-orally; it causes acute disease and does not become chronic. IgM anti-HAV indicates acute infection, and IgG anti-HAV indicates immunity.

Hepatitis B is an enveloped partially double-stranded DNA virus transmitted through blood, sex, or perinatal exposure. HBsAg indicates current infection. Anti-HBs indicates recovery or vaccination. Anti-HBc IgM indicates acute infection or the window period; anti-HBc IgG indicates prior exposure and persists after infection but is not produced by vaccination. HBeAg indicates high infectivity. Chronic HBV increases risk of cirrhosis and hepatocellular carcinoma partly through chronic inflammation and viral DNA integration.

Hepatitis C is an enveloped RNA virus transmitted mainly through blood exposure and often becomes chronic; it is associated with mixed cryoglobulinemia, membranoproliferative glomerulonephritis, porphyria cutanea tarda, lichen planus, and hepatocellular carcinoma through chronic cirrhosis. Hepatitis D is a defective RNA virus that requires HBsAg; coinfection can be severe, and superinfection in chronic HBV has high risk of fulminant hepatitis. Hepatitis E is fecal-oral and can be severe in pregnancy. Biliary disease connects stone chemistry to anatomy.

Cholesterol stones form when cholesterol exceeds bile salt and phospholipid solubilizing capacity. Risk increases with estrogen, pregnancy, obesity, rapid weight loss, age, female sex, ileal disease or resection, and gallbladder hypomotility. Black pigment stones form from calcium bilirubinate in sterile gallbladder bile, often with chronic hemolysis or cirrhosis. Brown pigment stones form in infected ducts due to bacterial beta-glucuronidase deconjugating bilirubin. Cystic duct obstruction causes biliary colic or acute cholecystitis with right upper quadrant pain, fever, leukocytosis, and Murphy sign.

Common bile duct obstruction causes jaundice and cholestatic labs; ascending cholangitis adds fever, jaundice, and right upper quadrant pain from infected obstructed bile. Gallstone ileus occurs when a cholecystoenteric fistula lets a large stone obstruct bowel, classically near the ileocecal valve. Pancreatitis is autodigestion from premature enzyme activation. Trypsinogen activation within acinar cells activates other zymogens, causing fat necrosis, hemorrhage, inflammation, and systemic cytokine release. Gallstones and alcohol are common causes.

Gallstones transiently obstruct the ampulla, while alcohol increases protein-rich pancreatic secretions, sphincter of Oddi spasm, and direct acinar toxicity. Hypertriglyceridemia, hypercalcemia, trauma, drugs, ERCP, and infections are additional causes. Acute pancreatitis presents with epigastric pain radiating to the back, nausea, elevated lipase, and sometimes hypocalcemia from fat saponification. Severe disease can cause ARDS, shock, renal injury, pseudocyst, necrosis, and infection.

Chronic pancreatitis is irreversible fibrosis, ductal distortion, calcifications, chronic pain, exocrine pancreatic insufficiency, and diabetes from islet injury. Steatorrhea appears only after major loss of exocrine reserve because pancreatic enzymes are produced in excess. Pancreatic insufficiency causes low fecal elastase, fat malabsorption, weight loss, and deficiency of vitamins A, D, E, and K. Cystic fibrosis causes thick secretions that obstruct pancreatic ducts, producing exocrine insufficiency in children, meconium ileus, and fat-soluble vitamin deficiency.

Pancreatic adenocarcinoma usually arises from ductal epithelium and is associated with smoking, chronic pancreatitis, diabetes, and age. Tumors in the head of the pancreas obstruct the common bile duct, causing painless jaundice, pruritus, pale stools, dark urine, and sometimes a palpable nontender gallbladder. Nutrition physiology is tested through absorption site, storage, and enzyme cofactor function. Thiamine is required for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, branched-chain alpha-ketoacid dehydrogenase, and transketolase.

Deficiency causes Wernicke encephalopathy, Korsakoff syndrome, beriberi, and lactic acidosis; give thiamine before glucose in high-risk patients because carbohydrate metabolism can worsen deficiency. Niacin deficiency causes pellagra: dermatitis, diarrhea, dementia, and sometimes death. Vitamin B6 deficiency can cause sideroblastic anemia, neuropathy, seizures, and isoniazid toxicity risk. Folate deficiency causes megaloblastic anemia with no neurologic deficits and is associated with neural tube defects.

B12 deficiency causes megaloblastic anemia plus subacute combined degeneration from impaired myelin maintenance, with methylmalonic acid and homocysteine elevation. Vitamin C deficiency impairs collagen hydroxylation, causing bleeding gums, perifollicular hemorrhage, poor wound healing, and corkscrew hairs. Vitamin A deficiency causes night blindness and squamous metaplasia. Vitamin D deficiency causes hypocalcemia, secondary hyperparathyroidism, rickets, osteomalacia, and proximal muscle weakness.

Vitamin E deficiency causes neurologic dysfunction, hemolytic anemia, and posterior column or spinocerebellar findings. Vitamin K deficiency impairs gamma-carboxylation of factors II, VII, IX, X and proteins C and S, prolonging PT first because factor VII has a short half-life. Bariatric surgery changes physiology by restriction, malabsorption, and altered incretin signaling. Roux-en-Y gastric bypass reduces acid and intrinsic factor exposure, bypasses duodenum and proximal jejunum, increases GLP-1, and can cause dumping syndrome from rapid hyperosmolar delivery to small bowel.

Early dumping causes cramping, diarrhea, tachycardia, and flushing; late dumping causes hypoglycemia from exaggerated insulin release. Common deficiencies after bypass include iron, B12, folate, calcium, vitamin D, and thiamine, so neurologic symptoms after vomiting or rapid weight loss should trigger concern for thiamine deficiency.